Method of producing grids for electron tubes



Oct. 6, 1970 HIDEO IWAYANAGI 3,531,839

METHOD OF PRODUCING GRIDS FOR ELECTRON TUBES Original Filed Nov. 6, 1963 Fig.

3 j: V. i 4 'a I! Fig. 4

INVENTOR H/DEa I wHY/Mn 6/ ATTORNEY Patented Oct. 6,, 1970 .5. Cl. 2925.16 6 Claims ABSTRACT OF THE DISCLOSURE This application discloses a method of manufacturing a grid construction of the frame grid type wherein first and second grids of fine wires are mounted in spaced parallel relationship and in perfect alignment to common frame members.

This is a division of application, ,Ser. No. 321,734, filed Nov. 6, 1963, now Pat. 3,316,438.

The present invention relates to an improvement in the method of manufacture of grid assemblies incorporated in electron tubes.

In the manufacture of a beam tube having a high mutual conductance, spacings between a cathode and grids are made generally smaller in order to obtain a high perveance. In this case, the effect of a periodic electric field induced by the grid wires is exerted to such a great extent that the three-halves power law is no longer effective at a point of low anode current due to the so-called Inselbildung effect, and any increase in the mutual conductance is thereby limited.

In order to minimize the efiect of such periodic electric field, pitches of the grids must be made small. For this, in the beam tube, it is necessary to adjust or align the relative positions of the No. 2 grid wires to the No. 1 grid wires. In a conventional manner of forming the grid assemblies, it has been a matter of difliculty to provide complete alignment of the grid wires as will be described later. Further, the accurate alignment of the grid wires has been extremely diflicult as the pitch of the grid wires becomes remarkably small.

The present invention aims at obviating such difficulties, and has for its object to provide a beam tube having an improved grid structure with an extremely high mutual conductance.

According to the invention, there is provided a method of manufacture of an improved grid block being composed of two grid assemblies each comprising a No. 1 grid, a No. 2 grid and ceramic supports therefor, said No. 1 grid being firmly fixed on one face of said ceramic supports, and said No. 2 grid being firmly fixed on the other face of said ceramic supports in such a manner that grid wires of the respective grids are in complete alignment with each other.

There are other objects and particularities of the invention which will be obvious from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view showing a cathode-grid assembly of a beam tube of conventional prior art structure,

FIG. 2 is a plan view of the cathode-grid assembly of FIG. 1;

FIG. 3 is a perspective view of a cathode-grid block which may be made according to the invention comprising an assembly of No. 1 and No. 2 grids and a cathode;

FIG. 4 is a perspective view of the grid assembly formed in accordance with the invention when viewed from the side of an anode;

FIG. 5 is a view similar to FIG. 4 but viewed from the side of a cathode;

FIG. 6 is a plan view of the electrodes as assembled by the use of insulating spacer discs; and

FIG. 7 is an explanatory view showing a manner of caging.

In FIGS. 1 and 2, there is shown a conventional prior art structure of a grid assembly wherein No. 1 grid wires 2 and No. 2 grid wires 4 are separately supported by supporting rods 1 and 3, respectively. Centrally of the grid structure, there is disposed a cathode 5. The No. 1 and No. 2 grids are thus formed by the grid wires 2 and 4 wound about the grid supports 1 and 3, which may consist, for example, or metal rods. The grid wires 2 and 4 are ordinarily wound in a manner such that they are spaced apart by a similar pitch or by a difierent pitch depending upon the expected difference in thermal expansion of the grid supports 1 and 3, respectively, to insure the alignment between the grid wires 2 and 4. However, the grid wires in the known constructions become misaligned during the operation of the electron tube, and the accurate alignment attained during the assembling is entirely lost once the electron tube is placed in operation. Provision of the different pitch is also not effective to insure complete alignment under all operating conditions. Further, the alignment of the No. 1 and No. 2 grids is generally made during the assembling of the grids together with the cathode 5 and other elements, but this operation becomes exceedingly difficult as the pitch of the grid wires is made extremely small.

Such difficulty is obviated by an improved grid structure manufactured according to the invention. FIGS. 3-5 show a grid assembly of an improved structure fabricated in accordance with the invention. Grid supports 12 are formed by ceramic rods and have a cross section which can provide a desired degree of spacing between No. 1 grid 13 and No. 2 grid 14. The ceramic rods may have a cross section of any suitable shape such as rectangular or any other shape. On opposite sides of each ceramic rod 12, there are provided metalized surfaces 15 and 16 of an elongated and narrow shape which can be produced by sintering a suitable metal such as molybdenum onto each ceramic rod 12. It is needless to say that the metalized surfaces 15 and 16 disposed on the back and front sides, respectively, of the ceramic rods 12 must be electrically insulated from each other.

As shown in FIGS. 4 and 5, the metalized surfaces 15 and 16 on the back and front sides of the ceramic rods 12 are staggered relative to each other so that interelectrode capacitance can be elfectively reduced. In straddling relation to the opposite ceramic rods 12, there are provided No. 1 and No. 2 grid wires 13 and 14, which are firmly fixed on the ceramic rods 12 in accordance with the invention in the following manner: An electrically conductive wire, which may be coated with a suitable metal as, for example, by gold plating, is wound completely around and partly in contact with the ceramic rods 12 with zero pitch to form loops in spaced relation along the entire length of the rods in such a manner that the pairs of opposing portions of the grid wire loops between the rods are in first and second parallel grid planes respectively, and each of the pairs of opposing portions are parallel with each other and are in a diflerent plane perpendicular to the grid planes. Such grid wire loops may be formed by the conventional conductor wiring technique commonly known to one in the art. For example, each turn of the winding may be formed such that opposing portions of the turn between the rods is in the same plane perpendicular to the grid planes for mutual and complete alignment, and one of the end portions of the turn which are in contact with the outer face of the rods is so formed so as to be concurrent with the starting or ending point of an adjacent turn so as to provide the spaced loops. Then the plated metal is heated to a molten state at a predetermined temperature to thereby obtain soldered connections between the grid wires and the metalized surfaces and 16 on the ceramic rods 12. After soldering, any excess of the grid wires on the sides of the ceramic rods 12 is cut off.

According to such manner of fabrication, it is easy to maintain satisfactory alignment of the grid wires 13 and 14 in the assembly of No. 1 and No. 2 grids. To provide proper reinforcement to the two grid supports 12, a metal strip 17 is fitted to connect the upper ends of the supports 12. For the lower ends of the supports 12, a metal strip 17 is likewise fitted. The metal strips may be soldered to the supports 12 prior to or simultaneously with the soldering of the grid wires on the suports 12, or may be dispensed with when the grid wires 13 and 14 are strong enough for supporting the ceramic supports 12. Or in place of the pair of ceramic rods 12 reinforced with the metal strips 17, a unitary body of a ceramic frame may be used.

FIG. 3 illustrates a cathode-grid block as assembled from two grid assemblies in accordance with the invention. The cathode-grid block shown corresponds to the cathode-grid assembly as shown in FIGS. 2. In FIG. 3, there is'shown a cathode 11 disposed between the two grid assemblies comprising the No. 1 and No. 2 grids. The No. 2 grids are connected with each other by a metal ribbon 18 to form a single grid. There are also shown a No. 2 grid connector 19, No. 1 grid connectors 20 and a cathode connector 21.

FIG. 6 shows an arrangement of electrodes wherein the cathode-grid block of FIG. 3 is shown as assembled therein with the use of insulating spacer discs such as of mica. Anodes 22 are supported by anode supports 23, and cage mica plates 24 have slits 29 and perforations 28 formed therethrough to receive therein the anodes 22 and the anode supports 23, respectively. The cage mica plates 24 have also slits 26 and 27 which are sized to suit the dimensions of the cathode 11 and the grid supports 12, respectively. The cage mica plates 24 may preferably split into halves as best shown in FIG. 7 so that the grid assemblies as shown in FIGS. 4 and 5 can be snugly fit in the slits 27 in the assembled state by the use of a suitable jig. After all the electrodes have been fitted in the slits of the halves of the cage mica plates 24, these halves are assembled integrally to form the electrode assembly. Then a supporting mica plate is superimposed on the cage mica plate 24, and the anode supports 23 are inserted into the perforations 28 to firmly fix the entire assembly.

Thus, according to the invention, complete alignment between the No. 1 grids 13 and the No. 2 grid 14 can be obtained even with an extremely fine pitch of the grid wires, and misalignment due to thermal expansion of the grid supports 12 can be entirely eliminated; Therefore, it is possible to fabricate beam tubes having a high mutual conductance and having an extremely small spacing between the cathode 11 and the grid structure.

I claim:

1. The method of producing a grid assembly for an electron tube consisting of a pair of support rods of an insulating material having first and second plural grid wires secured thereto in first and second respective parallel planes with respective grid wires in each plane being in complete alignment, the steps thereof comprising:

coating each of said support rods with continuous metal layers at diametrically opposite points along the entire length thereof,

supporting said rods in spaced parallel relationship,

winding 21 grid Wire completely around and partly in contact with the combination of said pair of support rods with zero pitch to form loops in spaced relation along the entire length of said rods in a manner that the pairs of opposing portions of said grid wire loops between said support rods are in first and second parallel grid planes respectively, and each of said pairs of opposing portions are parallel with each other and are in a different plane perpendicular to said grid planes,

heating said combination to a temperature where said grid wire loops are soldered to the associated metal layers, and

removing undesirable parts of those portions of said grid wire loops which are in contact with said support rods so as to form pairs of spaced parallel grid wires on complete alignment.

2. The method of producing a grid assembly for an electron tube consisting of a pair of support rods of an insulating material having first and second plural grid wires secured thereto in first and second respective parallel planes with respective grid wires in each plane being in complete alignment, the steps thereof comprising:

providing each of said support rods with layers of electrically conductive material at diametrically opposite points along the length thereof,

supporting said rods in spaced parallel relationship,

forming a plurality of grid wire loops around and partly in contact with the combination of said pair of support rods in spaced relation along the length of said rods provided with said layers in a manner that the pairs of opposing portions of said grid wire loops between said support rods are in first and second parallel grid planes respectively, and each of said pairs of opposing portions are parallel with each other and are in a different plane perpendicular to said grid planes,

securing said grid wire loops to said layers of electrically conductive material, and

removing undesirable parts of those portions of said grid wire loops which are in contact with said support rods so as to form pairs of spaced parallel grid wires in complete alignment.

3. The method defined in claim 2 wherein said electrically conductive layers are provided on said support rods by selective coating so as to leave diametrically opposite surfaces of each rod exposed.

4. The method defined in claim 2 wherein said grid wire loops are secured to said layers of electrically conductive material by heating said combination to a temperature where said grid wire loops are fused to said metal layers.

5. The method defined in claim 2 wherein prior to said winding said support rods are supported in spaced parallel relationship with corresponding layers thereon falling in spaced parallel planes.

6. The method defined in claim 2 wherein said loops are formed by winding a continuous grid wire around said pair of support rods with Zero pitch.

References Cited UNITED STATES PATENTS 2,497,066 2/ 1950 Brennan 317-58 XR 2,906,299 9/1959 Brooke --71.5 3,196,907 5/1962 Noiles et al 1407l.5 3,262,647 7/1966 Harrison 14071.5 XR 15,278 1/ 1922 Langmuir 313-350 XR 2.415,? 2/1947 McIntosh 2925.16 XR 2,500,355 3/1950 Haas 2925.16 XR 2,503,806 4/1950 Diggle 2925.16 XR 2,520,016 8/1950 Ronci et a1. 2925.16 XR 2,818,522 12/1957 Wheeler 2926.16 XR FOREIGN PATENTS 1,064,154 8/1959 Germany.

1,062,347 7/ 1959 Germany.

740,243 11/ 1955 England.

CHARLIE T. MOON, Primary Examiner R. B. LAZARUS, Assistant Examiner 

